Coping strategies in response to different levels of elevated water hardness in channel catfish (Ictalurus punctatus): Insight into ion-regulatory and histopathological modulations.

Water hardness above the optimal level can incite toxic effects in fish, which are often species specific. Hence, we aimed at obtaining insights on the potential effects of elevated water hardness as well as coping strategies in channel catfish (Ictalurus punctatus). First, a toxicity assay was performed where the 96 h-LC50 was calculated as 4939 mg/L CaCO3. Thereafter, to gain knowledge on the underlying adaptive strategies to high water hardness, fish were exposed to seven hardness levels (150, 600, 1000, 1500, 2000, 3000 and 4000 mg/L CaCO3 at pH 8.15) for 15 days. Results showed that branchial activities of Ca2+-ATPase and Na+/K+-ATPase, which facilitate Ca2+ uptake, reduced starting respectively from 1000 mg/L and 1500 mg/L CaCO3. Nevertheless, Ca2+ burden in plasma and tissue (gills, liver and intestine) remained elevated. Hardness exposure also disturbed cations (Na+, K+, Mg2+) and minerals (iron and phosphorus) homeostasis in a tissue-specific and dose-dependent manner. Both hemoglobin content and hematocrit dropped significantly at 3000-4000 mg/L CaCO3, with a parallel decline in iron content in plasma and gills. Muscle water content rose dramatically at 4000 mg/L CaCO3, indicating an osmo-regulation disruption. Higher hardness of 3000-4000 mg/L CaCO3 also incited a series of histopathological modifications in gills, liver and intestine; most likely due to excess Ca2+ accumulation. Overall, these data suggest that channel catfish can adapt to a wide range of elevated hardness by modulating Ca2+ regulatory pathways and histomorphological alterations, however, 1500 mg/L CaCO3 and above can impair the performance of this species.

Effects of bioprocessed soybean meal and nucleotide supplementation on growth, physiology and histomorphology in largemouth bass, Micropterus salmoides, juveniles.

In this 8-week feeding trial, the effects of nucleotide (N) supplementation (at 0.05%) were compared in diets with conventional soybean meal (CSBM or CSBM + N) versus bioprocessed SBM (BSBM or BSMB + N) on largemouth bass, Micropterus salmoides, juveniles. A total of five isonitrogenous and isolipidic diets were formulated, with the control diet being fishmeal-based. Growth, feeding efficiency, proximate composition, hepatic expression of genes involved in lipid metabolism and growth as well as liver/intestinal histopathology were assessed. Results showed that growth was significantly higher in fish fed the control diet, but there was no significant effect of SBM type or nucleotide supplementation on growth, feeding efficiency, or proximate composition. Hepatic expression of growth hormone (GH), insulin-like growth factor I (IGFI), superoxide dismutase (SOD), fatty acid synthase (FASN) and cholesterol 7 alpha-hydroxylase (CYP7A1) were unaffected by the diets. Tumor necrosis factor alpha (TNF-α) and transforming growth factor beta (TGF-ß) were significantly downregulated and upregulated, respectively, in the SBM-based treatments compared with the control. The intestinal villi were significantly shorter and wider in fish fed the CSBM diet compared to the other treatments. The villi height and width were similar between the control and those fed the BSMB + N diet. It may be possible that the unaffected growth by nucleotides were due to an insufficient dose and/or undisrupted nucleotide synthesis due to being cultured under good conditions. Meanwhile, the unaffected growth in the SBM treatment could indicate a tolerance of M. salmoides to plant proteins and associated antinutritional factors. Nevertheless, BSBM and/or nucleotides appeared to mitigate some adverse effects of dietary SBM to the intestinal histomorphology in M. salmoides.